It is known in the engine art to actuate valves with lost motion hydraulic actuators in place of conventional valve lifters and to provide a solenoid control valve, preferably with electronic control, for controlling the intake of fluid to and/or exhaust of fluid from the hydraulic actuators for varying the timing and/or lift of the valves in a desired manner. Systems and actuators for accomplishing such purposes are well known in the prior art. For example:
U.S. Pat. No. 4,615,306 Wakeman issued Oct. 7, 1986, shows multiple valves, associated with different engine cylinders and acting with different cam lift timings, having actuators which are controlled by a single solenoid valve and wherein discharged fluid is recirculated to the intakes of the other actuators;
U.S. Pat. No. 4,887,562 Wakeman, issued Dec. 19, 1989, discloses multiple intake or exhaust valves of a single cylinder actuated by a single cam through a combined actuator including dual actuating pistons with a hydraulic connection between them;
U.S. Pat. No. 4,930,465 Wakeman et al. shows a system in which each valve is controlled by a separate actuator and an associated solenoid valve, and fluid is both discharged from and delivered to each actuator through the same conduit;
U.S. Pat. No. 5,158,048 Robnett et al. discloses an actuator construction including damping; and
U.S. Pat. No. 5,216,988 Taxon illustrates an actuator arrangement for overhead cam engines with a system wherein inlet fluid is fed to the actuators separately from the discharge fluid that is controlled by an electronically actuated solenoid valve.
Of these patents, only 4,887,562 contemplates driving two similarly timed valves in the same cylinder with a common control valve. But it includes provision of hydraulic actuating means in place of more conventional engine components. Alternative means, requiring less modification of an engine to accommodate lost motion control of multiple valves in a single cylinder having identical or similar valve open periods, are considered desirable.
In the development of such arrangements, we proposed a system, shown in FIG. 1 of the drawings, in which an engine 10 having a plurality of cylinders 12 is provided with at least two inlet valves 14 for each cylinder. The valves 14 are each actuated by a separate hydraulic actuator 16 driven by a separate cam 18, both cams being preferably located on the same camshaft and having identical lift curves. The actuators shown are, for example, of the type shown in U.S. Pat. No. 5,216,988, but could be of any suitable type having a similar function. The valves 14 could instead be exhaust valves and the cams 18 could have overlapping valve timing with slightly different lift curves if desired, although identical opening times and lift curves are intended in the present instance.
Fluid, such as engine oil, is provided from a pressure source, such as the engine oil system, through a check valve 20 and inlet passage 22 connecting with one of the actuators 16. A connecting passage 24 extends between the two actuators 16 to carry fluid from one to the other. A discharge passage 26 connects the other of the actuators 16 with a solenoid valve 28. When opened, valve 28 discharges oil from the actuators to a sump 30 of the engine oil system.
The solenoid valve is preferably controlled by an electronic control unit, not shown, in a manner similar to that indicated in the previously discussed patents. Thus, when the solenoid valve is closed, the actuators 16 are filled with hydraulic fluid which is trapped therein. The trapped fluid provides a hydraulic link through which the actuators 16 are able to actuate the valves 14 with the lift and timing predetermined by the lift curves of their respective cams 18. In order to vary the valve timing and/or lift, the solenoid valve 28 is actuated at predetermined intervals to allow the discharge of oil from the system, collapsing the hydraulic link and allowing the valves 14 to be closed by their respective valve springs 32, not shown. Subsequent closure of the solenoid valve 28 allows refilling of the actuators 16, allowing them to again open the valves 14 on the following cycle.
While the arrangement disclosed above appears adequate for obtaining the desired results, it was found in testing such an arrangement that pressure pulses developed in the system were transmitted between the two hydraulically linked actuators 16 and caused erratic valve opening and closing action of the valves 14. An improved system retaining the features of simplicity and low cost was accordingly desired.